Allow specifying buildarch on the command line (#771382)

Some repos may contain anaconda packages for more architectures,
so it's not possible to get the right buildarch.
This patch allows optional specifying of the buildarch on the
command line when running lorax.
If the buildarch is not specified manually, lorax tries to get
it from the anaconda package as before.
If there's no anaconda package in the repository, don't fallback
to the system architecture and continue, because this is pointless.
We need the anaconda package.

src/pylorax/__init__.py

@@ -125,7 +125,7 @@ class Lorax(BaseLoraxClass):
         logger.addHandler(fh)
 
     def run(self, ybo, product, version, release, variant="", bugurl="",
-            isfinal=False, workdir=None, outputdir=None):
+            isfinal=False, workdir=None, outputdir=None, buildarch=None):
 
         assert self._configured
 
@@ -163,8 +163,11 @@ class Lorax(BaseLoraxClass):
         self.inroot = ybo.conf.installroot
         logger.debug("using install root: {0}".format(self.inroot))
 
+        if not buildarch:
+            buildarch = get_buildarch(ybo)
+
         logger.info("setting up build architecture")
-        self.arch = ArchData(get_buildarch(ybo))
+        self.arch = ArchData(buildarch)
         for attr in ('buildarch', 'basearch', 'libdir'):
             logger.debug("self.arch.%s = %s", attr, getattr(self.arch,attr))
 
@@ -252,8 +255,7 @@ def get_buildarch(ybo):
             buildarch = anaconda.arch
             break
     if not buildarch:
-        # fallback to the system architecture
-        logger.warning("using system architecture")
-        buildarch = os.uname()[4]
+        logger.critical("no anaconda package in the repository")
+        sys.exit(1)
 
     return buildarch

src/sbin/lorax

@@ -70,6 +70,8 @@ def main(args):
     optional.add_option("-e", "--excludepkgs", default=[],
             action="append", metavar="STRING",
             help="package glob to exclude (may be listed multiple times)")
+    optional.add_option("--buildarch", default=None,
+            help="build architecture", metavar="STRING")
 
     # add the option groups to the parser
     parser.add_option_group(required)
@@ -121,7 +123,7 @@ def main(args):
     lorax.configure(conf_file=opts.config)
     lorax.run(yb, opts.product, opts.version, opts.release,
               opts.variant, opts.bugurl, opts.is_beta,
-              workdir=tempdir, outputdir=outputdir)
+              workdir=tempdir, outputdir=outputdir, buildarch=opts.buildarch)
 
 
 def get_yum_base_object(installroot, repositories, mirrorlists=[],