Bug 945222 - Make test update script more flexible to work around the absence of try.

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extra : rebase_source : a4c685f016331f0fb1ffed809f0ba1adae6c2b11
Bug 945222 - Update web-platform-tests to revision 60cfc669eca9548dbaea4782767c252b094d15a0

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extra : rebase_source : 06ac875894afd506c5a8b978397244d290aaed1e