Allow plugins to use self-provided licenses for used Maven Jars

maven_jar only allowed to use licenses that were defined in
'//lib:'. But plugins may need further licenses that are not yet in
core (E.g.: plugins/its-jira relies on a jar with CPL1.0
license). Since, plugins cannot add rules underneath '//lib:', we add
the local_license parameter to maven_jar, which allows plugins to use
licenses from ':' instead of '//lib:'.

Change-Id: Icc40c413eed65a0b6e3003021050d91086ca4c34

lib/maven.defs

diff --git a/lib/maven.defs b/lib/maven.defs
index adce2a5..f11bd3c 100644
--- a/lib/maven.defs
+++ b/lib/maven.defs
@@ -42,7 +42,8 @@
     sha1 = '', bin_sha1 = '', src_sha1 = '',
     repository = MAVEN_CENTRAL,
     attach_source = True,
-    visibility = ['PUBLIC']):
+    visibility = ['PUBLIC'],
+    local_license = False):
   from os import path
 
   parts = id.split(':')
@@ -91,7 +92,10 @@
     cmd = ' '.join(cmd),
     out = binjar,
   )
-  license = ['//lib:LICENSE-' + license]
+  license = ':LICENSE-' + license
+  if not local_license:
+    license = '//lib' + license
+  license = [license]
 
   if src_sha1 or attach_source:
     cmd = ['$(exe //tools:download_file)', '-o', '$OUT', '-u', srcurl]