New osc plugin 'cycle': help visualizing build cycles

This new plugin creates dot files, visualizing the relation between the
package speciied on the command line. A major use case is visualizing
build cycles that are reported by OBS, but often not very clear to debug.

osc-cycle.py

@@ -0,0 +1,41 @@
+# Copyright (C) 2017 SUSE Linux Products GmbH
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+import osc.core
+
+def do_cycle(self, subcmd, opts, *args):
+    """${cmd_name}: Try to visualize build dependencies between the package list specified
+
+    Examples:
+    osc cycle <pkg1> <pkg2> <pkg3>    # outputs a dot file showing the relation between the listed packages
+
+    """
+
+    if len(args) == 0:
+        print ("No packages were specified, no chain to draw")
+
+    apiurl = self.get_api_url()
+
+    print ("digraph depgraph {")
+    for pkgname in args:
+        print ("\"%s\"" % pkgname)
+        deps = ET.fromstring(get_dependson(apiurl, "openSUSE:Factory", "standard", "x86_64", [pkgname]))
+
+        pkg = deps.find('package')
+        for deps in pkg.findall('pkgdep'):
+            if deps.text in args:
+                print ("\"%s\" -> \"%s\"" % (deps.text, pkgname))
+    print ("}")