oe-build-perf-report: Allow commits from different branches

The code won't currently allow comparisions of two commits on different
branches even if the commits are specified by their hashes.

This updates the code to search two branches for any relavent commits,
hence allowing comparisions to be made. A particularly useful case is
master vs. master-next for example.

(From OE-Core rev: 2d835bb1570c515ae501442f3ce19fae8e249b27)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oe-build-perf-report

@@ -542,6 +542,7 @@ Examine build performance test results from a Git repository"""
                        help="Tag name (pattern) for finding results")
     group.add_argument('--hostname', '-H')
     group.add_argument('--branch', '-B', default='master')
+    group.add_argument('--branch2')
     group.add_argument('--machine', default='qemux86')
     group.add_argument('--history-length', default=25, type=int,
                        help="Number of tested revisions to plot in html report")
@@ -579,6 +580,10 @@ def main(argv=None):
 
     revs = get_test_revs(repo, args.tag_name, hostname=args.hostname,
                          branch=args.branch, machine=args.machine)
+    if args.branch2:
+        revs = revs + get_test_revs(repo, args.tag_name, hostname=args.hostname,
+                             branch=args.branch2, machine=args.machine)
+
     if len(revs) < 2:
         log.error("%d tester revisions found, unable to generate report",
                   len(revs))