Fix max bmc dump size test
Fix max bmc dump size test

Changes:
    - Added variable to allow user driven number of dumps to create.
    
Tested:
    Ran successfully , example bellow
    robot -v OPENBMC_HOST:xxx.xx.xx.xx -v BMC_MAX_DUMP_COUNT:1000
          -v BMC_DUMP_TOTAL_SIZE:409600
          --include Verify_Maximum_BMC_Dump_Creation
          redfish/managers/test_bmc_dumps.robot 


Change-Id: I989dc6dc4fa12530fbb2b95e6d17e198632586c1
Signed-off-by: manashsarma <bc095463df3ac81e71d6b05cdcfc30e87ec3c38e@in.ibm.com>

openbmc/openbmc-test-automation,openbmc/openbmc-test-automation