ProcessUtil cleanup

- possible resource leak closed
- file content read uses now commons-lang FileUtils
- Added unit tests
CLOUDSTACK-4149
[upgrade][2.2.13 -> 2.2.14 -> 4.2][KVM] When we try to upgrade the KVM agent from 2.2.14 to 4.2 using the "U" option in install.sh script, management server also gets installed!