installFromYum: give more detailed error messages on gpg errors

repository.py

@@ -844,10 +844,38 @@ def updateInstallProgress(m):
                 total = 0
                 updateInstallProgress(m)
         rv = p.wait()
+        gpg_error_message = None
+
+            if stderr.find(' in import_key_to_pubring') >= 0:
+                gpg_error_message = "Signature key import failed"
+            # add any other instance of uncaught GpgmeError before this like
+            elif stderr.find('gpgme.GpgmeError: ') >= 0:
+                gpg_error_message = "Cryptography-related yum crash"
+
+            elif re.search("Couldn't open file [^ ]*/repodata/repomd.xml.asc", stderr):
+                # would otherwise be mistaken for "pubring import" !?
+                gpg_error_message = "No signature on repository metadata"
+            elif stderr.find('repomd.xml signature could not be verified') >= 0:
+                gpg_error_message = "Repository signature verification failure"
+
+            else:
+                match = re.search("Public key for ([^ ]*.rpm) is not installed", stderr)
+                if match:
+                    gpg_error_message = "Missing key for %s" % (match.group(1),)
+                match = re.search("Package ([^ ]*.rpm) is not signed", stderr)
+                if match:
+                    gpg_error_message = "Package not signed: %s" % (match.group(1),)
+                match = re.search(r" ([^ ]*): \[Errno [0-9]*\] No more mirrors to try", stderr)
+                if match:
+                    # rpm not found or corrupted/re-signed/etc
+                    gpg_error_rpm_not_found = match.group(1)
+                    gpg_error_message = "Cannot find valid rpm for %s" % (match.group(1),)
 
         if rv:
             logger.log("DNF exited with %d" % rv)
-            raise ErrorInstallingPackage("Error installing packages")
+            if gpg_error_message is None:
+                gpg_error_message = "Error installing packages"
+            raise ErrorInstallingPackage(gpg_error_message)
 
         shutil.rmtree(os.path.join(mounts['root'], cachedir), ignore_errors=True)