fcm make: build: fix etc files install

The configuration line `build.prop{class,file-she.script} = #!`
generated by the mirror step is causing the build of etc files to behave
incorrectly. This change hard codes `#!` in the pattern match. (It is
standard Unix, so is unlikely to ever change.)
Merge pull request #77 from matthewrmshin/fix-fcm-make-build-etc

fcm make: build: fix etc files install