[JENKINS-15904] Perforce plugin issues wrong error message when exception occurs on remote end

These changes improve the error messages logged to the user. P4.exe is run with '-v 1' and '-s' options. Also using just one p4 executor method. 

We are using recently new Jenkins core (1.454 and 1.492), I hope this works also with older cores.

Changes are actually done by my colleague so if you have questions I need to consult him.