MULE-7204 Use concurrent cache to correctly synchronize compilation, ii) avoid use of parserContext.createSubContext() as it causes concurrency issues and iii) add more through test.

(cherry picked from commit 00b396bc94b4bae2dfd9b360638a2bfacb398887)

Conflicts:
core/pom.xml
core/src/main/java/org/mule/el/mvel/MVELExpressionExecutor.java
core/src/main/java/org/mule/el/mvel/MVELExpressionLanguage.java
core/src/test/java/org/mule/el/mvel/MVELExpressionLanguageTestCase.java
distributions/standalone-light/assembly-whitelist.txt
distributions/standalone/assembly-whitelist.txt
pom.xml
tests/functional/src/test/java/org/mule/test/el/ExpressionLanguageConcur
rencyTestCase.java
Handle cases where UncheckedExecutionException wraps both checked and unchecked exception

(cherry picked from commit c172e42dbb7fba14dbaead9cbf06a19107aa72ec)
MULE-7312: Updated Guava to 16.0.1 to fix an incompatibility with the latest JDK7

(cherry picked from commit bdf05076a3cbed021525504f590942ab56124832)