Bug 922147 - Abstract password out of Android Sync auth flow. r=rnewman

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extra : amend_source : 785ee7294bce83665caa3d79ee2144644fc7b9b5
extra : histedit_source : b4b47d0903d6f94b8bd08b78654b4538d18e220f%2Cf89a9d672b5ac4e13481abfcc0f937182680eddd