bitbake: fetch2: Make SRCREV_FORMAT name substitution safer

bitbake: fetch2: Make SRCREV_FORMAT name substitution safer

The implementation of SRCREV_FORMAT has at least two issues:

 1. Given two names "foo" and "foobar" and SRCREV_FORMAT = "foo_foobar",
    "foo" might currently get substituted twice, and "foobar" not at
    all.

 2. If the revision substitued for some name happens to contain another
    name as a substring, then that substring might incorrectly get
    replaced.

Fix both issues by sorting the names with the longest ones first and
replacing all names at once with a regular expression. This was inspired
by
http://stackoverflow.com/questions/6116978/python-replace-multiple-strings.

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>