Unable to locate dependent libraries when absolute path is not given to the Server() instance

[vinayvennela]

If the browsermob-proxy path is added to $PATH, and the Server is initiated with
server = Server("browsermob-proxy") instead of server = Server("path/to/browsermob-proxy")

then the proxy server doesn't start.
A possible reason could be "Error: Unable to access jarfile /mnt/lib/browsermob-dist-2.1.4.jar

Root Cause:
Though it is implemented to check whether the executable is present in the $PATH or not, there is no way to set the path variable to the absolute path when we find the executable on the $PATH

[vinayvennela]

@AutomatedTester Have created the PR too, please review
#98

[vinayvennela]

@AutomatedTester Please review the PR.