icasefs: refactor "test-casecollision-merge.t" to reuse in succeeding fixes
This patch refactors "test-casecollision-merge.t" to increase
reusability in succeeding patches.
It is confirmed that changed test also can detect issue3370.
fixbundle() {
grep -v 'saving bundle' | grep -v 'saved backup' | \
grep -v added | grep -v adding | \
grep -v "unable to find 'e' for patching" | \
grep -v "e: No such file or directory"
}