Add --pkgarch option to build.py to specify the packaging architecture

pkg arch can be different to GOARCH.

Example: build for debian on raspberry pi. GOARCH will be arm
but the packaging architecture on debian will be armhf (arm
hard float). The --pkgarch option is passed to fpm to specify
the required architecture which is reflected in the package
manifest and also in the result filename.

closes #675

build.py

@@ -412,7 +412,7 @@ def generate_md5_from_file(path):
             m.update(data)
     return m.hexdigest()
 
-def build_packages(build_output, version, nightly=False, rc=None, iteration=1):
+def build_packages(build_output, version, pkg_arch, nightly=False, rc=None, iteration=1):
     outfiles = []
     tmp_build_dir = create_temp_dir()
     if debug:
@@ -461,6 +461,9 @@ def build_packages(build_output, version, nightly=False, rc=None, iteration=1):
                         current_location = os.path.join(current_location, name + '.tar.gz')
                     if rc is not None:
                         package_iteration = "0.rc{}".format(rc)
+                    saved_a = a
+                    if pkg_arch is not None:
+                        a = pkg_arch
                     if a == '386':
                         a = 'i386'
                     fpm_command = "fpm {} --name {} -a {} -t {} --version {} --iteration {} -C {} -p {} ".format(
@@ -472,6 +475,8 @@ def build_packages(build_output, version, nightly=False, rc=None, iteration=1):
                         package_iteration,
                         build_root,
                         current_location)
+                    if pkg_arch is not None:
+                        a = saved_a
                     if package_type == "rpm":
                         fpm_command += "--depends coreutils "
                         fpm_command += "--depends lsof"
@@ -506,6 +511,7 @@ def print_usage():
     print("\t --goarm=<arm version> \n\t\t- Build for specified ARM version (when building for ARM). Default value is: 6")
     print("\t --platform=<platform> \n\t\t- Build for specified platform. Acceptable values: linux, windows, darwin, or all")
     print("\t --version=<version> \n\t\t- Version information to apply to build metadata. If not specified, will be pulled from repo tag.")
+    print("\t --pkgarch=<package-arch> \n\t\t- Package architecture if different from <arch>")
     print("\t --commit=<commit> \n\t\t- Use specific commit for build (currently a NOOP).")
     print("\t --branch=<branch> \n\t\t- Build from a specific branch (currently a NOOP).")
     print("\t --rc=<rc number> \n\t\t- Whether or not the build is a release candidate (affects version information).")
@@ -532,6 +538,7 @@ def main():
     commit = None
     target_platform = None
     target_arch = None
+    package_arch = None
     nightly = False
     race = False
     branch = None
@@ -570,6 +577,9 @@ def main():
         elif '--version' in arg:
             # Version to assign to this build (0.9.5, etc)
             version = arg.split("=")[1]
+        elif '--pkgarch' in arg:
+            # Package architecture if different from <arch> (armhf, etc)
+            package_arch = arg.split("=")[1]
         elif '--rc' in arg:
             # Signifies that this is a release candidate build.
             rc = arg.split("=")[1]
@@ -703,7 +713,7 @@ def main():
         if not check_path_for("fpm"):
             print("!! Cannot package without command 'fpm'. Stopping.")
             return 1
-        packages = build_packages(build_output, version, nightly=nightly, rc=rc, iteration=iteration)
+        packages = build_packages(build_output, version, package_arch, nightly=nightly, rc=rc, iteration=iteration)
         # Optionally upload to S3
         if upload:
             upload_packages(packages, bucket_name=upload_bucket, nightly=nightly)