[MINOR] [CORE] Accept alternative mesos unsatisfied link error in test.

The IBM JVM reports an failed library load with a slightly different error message to Oracle's JVM.  Update the test case to allow for either form.

Author: Tim Ellison <tellison@users.noreply.github.com>
Author: Tim Ellison <t.p.ellison@gmail.com>

Closes #6119 from tellison/LibraryLoading and squashes the following commits:

2c5cd4e [Tim Ellison] Reduce assertion to check for the mesos library name
f48c194 [Tim Ellison] Split long line
b1079d7 [Tim Ellison] [MINOR] [CORE] Accept alternative mesos unsatisfied link error in test.

core/src/test/scala/org/apache/spark/SparkContextSchedulerCreationSuite.scala

@@ -159,7 +159,7 @@ class SparkContextSchedulerCreationSuite
       assert(sched.backend.getClass === expectedClass)
     } catch {
       case e: UnsatisfiedLinkError =>
-        assert(e.getMessage.contains("no mesos in"))
+        assert(e.getMessage.contains("mesos"))
         logWarning("Mesos not available, could not test actual Mesos scheduler creation")
       case e: Throwable => fail(e)
     }