Redmine#6189: Store the hardcoded bootstrap file in a variable

..instead of using it directly to prevent old GCCs from failing due to
fprintf usage as a macro

Modified by: Kristian Amlie <kristian.amlie@cfengine.com>
(cherry picked from commit f0ebf2388f4c135b3a07075a8418cd040d80da65)
Merge remote-tracking branch 'upstream/3.6.x' into 3.6.x