Code refactoring.

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
[JENKINS-22075] - Advanced null checks for missing tools (not finished)

Added checks of non-existent tools to the most of handlers

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
[JENKINS-22075] - Properly handle missing tools in CustomToolInstallWrapper

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
[JENKINS-18814] - Throw errors if the configured tool cannot be found
Merge pull request #15 from synopsys-arc-oss/master

[JENKINS-18814,JENKINS-22075] - Handling of deleted tools