RFR: JDK-8030794: Update configure to require jdk8 as boot

[Erik Joelsson]

There are now changes in jdk9 which prohibit the use of jdk7 as boot jdk 
(unless the update version is high enough). It's time we formally change 
the requirement from jdk7 to jdk8 by making configure require it.

Bug: https://bugs.openjdk.java.net/browse/JDK-8030794
Patch:

diff -r 1dfbd8aa5d3d common/autoconf/boot-jdk.m4
--- a/common/autoconf/boot-jdk.m4
+++ b/common/autoconf/boot-jdk.m4
@@ -82,10 +82,10 @@
              BOOT_JDK_VERSION=`"$BOOT_JDK/bin/java" -version 2>&1 | 
head -n 1`

              # Extra M4 quote needed to protect [] in grep expression.
-            [FOUND_CORRECT_VERSION=`echo $BOOT_JDK_VERSION | grep 
'\"1\.[789]\.'`]
+            [FOUND_CORRECT_VERSION=`echo $BOOT_JDK_VERSION | grep 
'\"1\.[89]\.'`]
              if test "x$FOUND_CORRECT_VERSION" = x; then
                AC_MSG_NOTICE([Potential Boot JDK found at $BOOT_JDK is 
incorrect JDK version ($BOOT_JDK_VERSION); ignoring])
-              AC_MSG_NOTICE([(Your Boot JDK must be version 7, 8 or 9)])
+              AC_MSG_NOTICE([(Your Boot JDK must be version 8 or 9)])
                BOOT_JDK_FOUND=no
              else
                # We're done! :-)