Delay calculation of offline storage path as long as is practically poss...

...ible.

This avoids calculating it incorrectly in the case that something later clobbers
argv, such as a zygote or booster-type mechanism.

Change-Id: Ifab16c7c94e9ee3fded0dfda2266a12c910858ee
Reviewed-by: Matthew Vogt <matthew.vogt@qinetic.com.au>
Reviewed-by: Martin Jones <martin.jones@jollamobile.com>