implement --list-tags option for builder

this should get plain list. One tag per each line. Eg.:
dist-5E-sw-1.3-candidate
dist-f13-sw-1.3-candidate

if run --list-tags --debug, it should list all tags with explanation
why it is included or not listed. E.g:
dist-5E-sw-1.3-candidate
dist-f13-sw-1.3-candidate whitelisted
dist-f14-sw-1.3-candidate blacklisted

src/tito/builder.py

@@ -179,6 +179,8 @@ class Builder(object):
             self._cvs_release()
         elif options.koji_release:
             self._koji_release()
+        elif options.list_tags:
+            self._list_tags()
 
         self.cleanup()
         return self.artifacts
@@ -358,6 +360,25 @@ class Builder(object):
 
             self._submit_build("koji", koji_opts, koji_tag)
 
+    def _list_tags(self):
+        """ Print tags to which we build this package. """
+        autobuild_tags = self.config.get("koji", "autobuild_tags")
+        koji_tags = autobuild_tags.strip().split(" ")
+        for koji_tag in koji_tags:
+            if self.config.has_option(koji_tag, "whitelist") and \
+                    self.project_name in self.config.get(koji_tag,
+                    "whitelist").strip().split(" "):
+                if 'DEBUG' in os.environ:
+                    koji_tag += ' whitelisted'
+            elif self.config.has_option(koji_tag, "blacklist") and \
+                    self.project_name in self.config.get(koji_tag,
+                    "blacklist").strip().split(" "):
+                if 'DEBUG' in os.environ:
+                    koji_tag += ' blacklisted'
+                else:
+                    continue
+            print koji_tag
+
     def _setup_sources(self):
         """
         Create a copy of the git source for the project at the point in time

src/tito/cli.py

@@ -345,6 +345,10 @@ class BuildModule(BaseCliModule):
                 action="store_true",
                 help="Release package only in Koji. (if possible)",
                 )
+        self.parser.add_option("--list-tags", dest="list_tags",
+                action="store_true",
+                help="List tags for which we build this package",
+                )
         self.parser.add_option("--upload-new-source", dest="cvs_new_sources",
                 action="append",
                 help=("Upload a new source tarball to CVS lookaside. "

tito.8.asciidoc

@@ -157,6 +157,11 @@ Release package only in CVS. (if possible)
 --koji-release::
 Release package only in Koji. (if possible)
 
+--list-tags::
+List tags for which we build this package. If you set --debug together
+with this option, you will see all tags and whether they are whitelisted
+or blacklisted.
+
 --upload-new-source='CVS_NEW_SOURCES'::
 Upload a new source tarball to CVS lookaside. (i.e.
 runs 'make new-sources') Must be used until 'sources'