Configure script should check that grpc-java plugin exists at the given path

[Alex Dumitru]

If i run

./configure --enable-rasnet --with-grpc-java-plugin=/tmp/nothere

the configure script says everything is ok. We should check if the plugin is actually there and report back.

[Dimitar Misev]

There is some issue with running ./configure on CentOS 6 (I can't generate RPMs) after this patch:

checking for boostlib >= 1.48... yes
./configure: line 13896: syntax error near unexpected token `else'
./configure: line 13896: `else'
error: Bad exit status from /var/tmp/rpm-tmp.x4I27p (%build)
RPM build errors:
    Bad exit status from /var/tmp/rpm-tmp.x4I27p (%build)
Child return code was: 1
EXCEPTION: Command failed. See logs for output.
 # bash --login -c /usr/bin/rpmbuild -bb --target x86_64 --nodeps  /builddir/build/SPECS/rasdaman.spec 
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/mockbuild/trace_decorator.py", line 84, in trace
    result = func(*args, **kw)
  File "/usr/lib/python2.7/site-packages/mockbuild/util.py", line 493, in do
    raise exception.Error("Command failed. See logs for output.\n # %s" % (command,), child.returncode)
Error: Command failed. See logs for output.
 # bash --login -c /usr/bin/rpmbuild -bb --target x86_64 --nodeps  /builddir/build/SPECS/rasdaman.spec 
LEAVE do --> EXCEPTION RAISED

[Dimitar Misev]

I submitted a fix which is strangely:

-    AC_CHECK_FILE("${GRPCCPPPLUGIN}", [] ,[AC_MSG_ERROR([..])])
+    AC_CHECK_FILE("${GRPCCPPPLUGIN}", , [AC_MSG_ERROR([..])])