SCRIPT: run-regtests: avoid calling awk to compute the version

SCRIPT: run-regtests: avoid calling awk to compute the version

For each test, the version number is evaluated using a call to awk,
which can be slow to start depending on the versions and OS. This is
only needed for a printf() call to keep only leading digits of each
component, multiply them by 1000 and pad them to 3 digits, something
that's clearly doable in plain shell in a portable way. This is what
this patch does, and it saves yet another 400 ms here on the full
test sequence.