Add regression test for JAVA_HOME override

Regression/java-home-override/bin/java

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+#!/bin/sh
+set -e
+echo DUMMY JAVA CALLED
+echo args: "$@"
+exit 42

Regression/java-home-override/main.fmf

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+summary: Maven JAVA_HOME override test
+description: |
+  Test whether Maven respects JAVA_HOME set by user.

Regression/java-home-override/runtest.sh

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+#!/bin/bash
+# Author: Mikolaj Izdebski <mizdebsk@redhat.com>
+. /usr/share/beakerlib/beakerlib.sh
+
+rlJournalStart
+
+  rlPhaseStartTest "display Maven version"
+    # No JAVA_HOME - use default Java
+    rlRun -s "mvn --version"
+    rlAssertGrep "Apache Maven" $rlRun_LOG
+    # JAVA_HOME set to a directory containing dummy Java script
+    rlRun -s "JAVA_HOME=$PWD mvn --version" 42
+    rlAssertGrep "DUMMY JAVA CALLED" $rlRun_LOG
+    rlAssertGrep plexus-classworlds $rlRun_LOG
+    # JAVA_HOME set to non-directory
+    rlRun -s "JAVA_HOME=/dev/null mvn --version" 1
+    rlAssertGrep "The JAVA_HOME environment variable is not defined correctly" $rlRun_LOG
+  rlPhaseEnd
+
+rlJournalEnd
+rlJournalPrintText