gcrypt: do not fail on version mismatch (bsc#906217)

Check for the minimum version we know to work and do not fail
if wicked is built with newer libgcrypt version than installed.
Trust the linker and the libgcrypt library versioning / soname.
Merge pull request #464 from mtomaschewski/gcrypt-version

gcrypt: do not fail on version mismatch (bsc#906217)