Set the releasever and install gpg keys when using --repo

This uses the --release value as the yum releasever so that $releasever
in a --repo will work.

It also turns on assumeyes so that any gpgkey entries in the .repo file
will be installed and used automatically if gpgcheck is enabled for the
repo.

Related: rhbz#1430479

src/sbin/lorax

@@ -199,7 +199,7 @@ def main(args):
     yb = get_yum_base_object(installtree, opts.source, opts.mirrorlist,
                              opts.repo_files,
                              yumtempdir, opts.proxy, opts.excludepkgs,
-                             not opts.noverifyssl)
+                             not opts.noverifyssl, opts.release)
 
     if yb is None:
         print("error: unable to create the yumbase object", file=sys.stderr)
@@ -237,7 +237,7 @@ def main(args):
 
 def get_yum_base_object(installroot, repositories, mirrorlists=[], repo_files=[],
                         tempdir="/var/tmp", proxy=None, excludepkgs=[],
-                        sslverify=True):
+                        sslverify=True, releasever=None):
 
     def sanitize_repo(repo):
         """Convert bare paths to file:/// URIs, and silently reject protocols unhandled by yum"""
@@ -269,6 +269,7 @@ def get_yum_base_object(installroot, repositories, mirrorlists=[], repo_files=[]
             "keepcache": 0,
             "gpgcheck": 0,
             "plugins": 0,
+            "assumeyes": 1,
             "reposdir": "",
             "tsflags": "nodocs"}
 
@@ -325,6 +326,8 @@ def get_yum_base_object(installroot, repositories, mirrorlists=[], repo_files=[]
     yb.preconf.fn = yumconf
     yb.preconf.root = installroot
     #yb.repos.setCacheDir(cachedir)
+    if releasever:
+        yb.preconf.releasever = releasever
 
     # Turn on as much yum logging as we can
     yb.preconf.debuglevel = 6