Increase timeout for slow tests on UnixBigMemBuild (#554)

test_lzma and test_bigmem require more time to be fully executed.
Increase the default timeout to allow these tests to pass.

master/custom/factories.py

@@ -267,6 +267,7 @@ class UnixBuildWithoutDocStrings(UnixBuild):
 class UnixBigmemBuild(UnixBuild):
     buildersuffix = ".bigmem"
     testFlags = ["-M60g", "-j4", "-uall,extralargefile"]
+    test_timeout = TEST_TIMEOUT * 4
     factory_tags = ["bigmem"]