Allow overridding "app_name" for "test" template on iOS.

Some downstream iOS unit tests requires the value of BUNDLE_ID_TEST_NAME
to correspond to the target name without any underscore, so let client
override the value of app_name until gyp support is dropped and the tests
can use the target name for value of BUNDLE_ID_TEST_NAME.

BUG=604692

Review-Url: https://codereview.chromium.org/2022813002
Cr-Commit-Position: refs/heads/master@{#396746}
1 file changed