Specify strstr strgob strglobin str_starts str_ends str_replace

As discussed in haraldh/dracut#15, solidifies the specification of strstr to be a literal string match, as it is in the C library. Changes call sites that used it as a glob match to use newly-added functions strglob or strglobin instead. The strglob function requires a glob to match all of the string; strglobin only requires a match in the string. Also tightens up str_starts, str_ends, and str_replace to do literal matches only. I did not find any call sites where these seemed to be used with globs.

I do not have all the prerequisites installed here to run the testsuite. It may be desirable to do that before merging. The changes are small and straightforward but in a variety of places. I have tested the new function definitions, and I have done a successful boot of my own box, but I have not run the full testsuite.

Resolves haraldh/dracut#15.