Fixed bug with NPE in case of empty tools list

Signed-off-by: Oleg Nenashev <nenashev@synopsys.com>
Merge pull request #3 from synopsys-arc-oss/bugfix-npe-for-emty-toolslist

Fixed bug with NPE in case of empty tools list (JENKINS-18481)
Merge pull request #2 from synopsys-arc-oss/master

Support of Variables in EXPORTED_PATHS and TOOL_HOME + bug fixes (JENKINS-14515 and JENKINS-17844)
Added support of global variables

Signed-off-by: Oleg Nenashev <nenashev@synopsys.com>
Modified description of the plugin

Signed-off-by: Oleg Nenashev <nenashev@synopsys.com>