Fix regex support in --only, --skipfile and --skiptest

[valentinogeron]

The regex support was added in:

• support regex in "--only" in runtest #9352
• Add --skipfile and --skiptest regex support. #9555
• Revert the attempt to fix cluster rebalance test (#10207) #10212

These commits break backword compatiblity with older versions.

This fix keeps the test suite infra compatible with old versions by
default. However, if you want regex, the string must start with /

[oranagra]

I'm not sure the approach of trying both is right.
It means we may skip something we didn't mean to skip.
I suppose the right thing to do is have an argument or prefix that indicate the type of string matching.

I'm AFK, but I suppose all of these got broken in 7.0, so maybe we should just "revert" it, and introduce it again properly.
I.e. Make the default as it was before, and the regex thing optional.

[oranagra]

I discussed this with Yossi, we decided to be compatible with old versions by default and if you want regex the string must start with /
@valentinogeron can you change your PR?

[valentinogeron]

I discussed this with Yossi, we decided to be compatible with old versions by default and if you want regex the string must start with / @valentinogeron can you change your PR?

@oranagra - yes