Fix NoClassDefFoundError and make delete methods throw MdbmNoEntryException

[hirkatou]

In java implementation,

NoClassDefFoundError occurs when deleteing non existing key.

testDeleteNoEntry(com.yahoo.db.mdbm.TestV4)  Time elapsed: 0.023 sec  <<< FAILURE!
java.lang.NoClassDefFoundError: com/yahoo/db/mdbm/exceptions/MdbmDeleteException
        at com.yahoo.db.mdbm.internal.NativeMdbmAccess.mdbm_delete(Native Method)
        at com.yahoo.db.mdbm.internal.NativeMdbmImplementation.delete(NativeMdbmImplementation.java:99)
        at com.yahoo.db.mdbm.TestSimpleMdbm.testDeleteNoEntry(TestSimpleMdbm.java:214)

This PR implements 2 points.

• Define MdbmDeleteException.
• Make delete methods throw MdbmNoEntryException when key is not exists.

[areese]

👍 Thanks.

[yahoocla]

CLA is valid!