If there's a global variable defining a path to maven/bin. Pipeline integration fails to setup the requested maven tool.

*Steps to Reproduce*

1.  Install two maven versions, say 3.5.3 and 3.5.4

2. Define a global variable PATH+MAVEN=/path/to/maven/3.5.3/bin

3. Create a pipeline that uses withMaven step selecting maven 3.5.4

Run sh "mvn --version"

We expect it to show selected version 3.5.4 but it will show 3.5.3