gm: add --ignoreTests flag

gm/tests/outputs/ignoring-one-test/output-expected/stdout

Index: gm/tests/outputs/ignoring-one-test/output-expected/stdout
===================================================================
--- gm/tests/outputs/ignoring-one-test/output-expected/stdout	(revision 0)
+++ gm/tests/outputs/ignoring-one-test/output-expected/stdout	(working copy)
@@ -1,8 +1,8 @@
 GM: These configs will be run: 8888 565
 GM: reading expectations from JSON summary file gm/tests/inputs/json/different-pixels.json
-GM: writing to gm/tests/outputs/compared-against-different-pixels-json/output-actual/writePath
-GM: writing mismatches to gm/tests/outputs/compared-against-different-pixels-json/output-actual/mismatchPath
-GM: writing images without expectations to gm/tests/outputs/compared-against-different-pixels-json/output-actual/missingExpectationsPath
+GM: writing to gm/tests/outputs/ignoring-one-test/output-actual/writePath

[epoger, 2013/09/18 18:57:41]

Patchset 2 also updates the output for the new gm self-test to pass (that output
will change again, once I actually implement the flag in gmmain)

+GM: writing mismatches to gm/tests/outputs/ignoring-one-test/output-actual/mismatchPath
+GM: writing images without expectations to gm/tests/outputs/ignoring-one-test/output-actual/missingExpectationsPath
 GM: drawing... selftest1 [300 200]
 GM: Ran 1 GMs
 GM: ... over  2 configs ["8888", "565"]