Enhance BMC error log utilities

  - Add keyword which obtains a dictionary containg the error logs.
  - Update the Error Logs Should Not Exist keyword to give a
     meaningful message other than 200 != 404.

Resolves openbmc/openbmc-test-automation#1306
Change-Id: I15582e64595c40537d92883675ca2c5e0b9074a3
Signed-off-by: Steven Sombar <ssombar@us.ibm.com>
2 files changed