[JENKINS-47793] - Jenkins master and agent configuration pages do not verify...

[JENKINS-47793] - Jenkins master and agent configuration pages do not verify negative executor numbers (#3141)

* Fixed Regexps for number & positive-number

* Progress saving

* Fix for validation

* bug fixing

* bug fixing

* Address comments

* Address comments

* Address comments from @jglick

* Whitespace cleanup

* Address comment for @jglick