Improve m2 discovery process

Description

Improve the m2 discovery process, m2 discovery is used for plugins/connectors loading.

Technical analysis

Actual discovery process:

1. Read talend.component.manager.m2.repository system property
2. Check if we're running in studio and uses its m2 if system property is not set to maven.repository=global
3. Parse maven's settings.xml (or if provided talend.component.manager.m2.settings) for checking if a property localRepository is defined
4. Fallbacks to ${user.home}/.m2/repository

We should improve at least by : 

• in settings.xml
  • evaluate system properties
  • evaluate env variables
• evaluate the ~ value in any properties content

And checking for maven env properties (ie $M2_HOME) should go after 3.

Final Implementation

The following chart is a representation of the solution HERE
Settings.xml parsing has been improving:

• evaluate system properties
• evaluate env variables|

New function implemented to evaluate the ~ value in any properties content