Replace grep -P with grep -E for compatibility on vCenter

[shrapnel55]

This will solve issue #9

This PR replaces all occurrences of grep -P with grep -E in find_brickstorm.sh. The reason for this change is that grep -P (Perl-compatible regex) is not supported on vCenter/Photon builds, as grep is compiled with --disable-perl-regexp. This causes the script to fail with errors like:
grep: support for the -P option is not compiled into this --disable-perl-regexp binary

Verified that grep -P is unavailable:

grep -P . /dev/null; echo $?  # exit code 2
grep --help | grep -E -- '-P|Perl|PCRE' || echo "-P not in help"

Confirmed that the pattern (..){0,5} works with Extended Regular Expressions (ERE):
printf 'aabbcc' | grep -Eq '(..){0,5}' && echo "ERE ok"

After replacing -P with -E, the script executed successfully without errors.

Why -E?
The script comment mentions grep -Pq for Perl-compatible regex to support (..){0,5}, but this is also supported by ERE. Unless the script intends to use PCRE-only features (lookarounds, \K, etc.), -E is a portable alternative.
Request for Feedback
If there is a specific reason why -P is required, please let me know. Otherwise, this change improves compatibility across environments where PCRE is disabled.

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