Adding Testcase Description field

[sidhujasminder]

What issues does this PR fix or reference?

Fix #309

Previous Behavior

No description Field in testcase definition file

New Behavior

Now the testcases can be defined in the following manner.

test_show_interfaces:
  - rpc: get-interface-information
  - kwargs:
      interface-name: lo0
  - iterate:
      xpath: physical-interface
      id: name
      tests:
         - no-diff: oper-status
           info: "Passed"
           err: "Failed"

test_show_interfaces_1:
  - rpc: get-interface-information
  - kwargs:
      interface-name: lo0
  - iterate:
      xpath: physical-interface
      id: name
      tests:
         - no-diff: oper-status
           info: "Passed"
           err: "Failed"
  - description: "This Test is for comparing the diff between the oper-status node in rpc get-interface-information."

**************************** Device: 10.204.49.97 ****************************
Tests Included: test_show_interfaces_1
Description: This Test is for comparing the diff between the oper-status node in rpc get-interface-information.
RPC is get-interface-information
Failed
FAIL | All "oper-status" is not same in pre and post snapshot [ 0 matched / 1 failed ]
Tests Included: test_show_interfaces
RPC is get-interface-information
Failed
FAIL | All "oper-status" is not same in pre and post snapshot [ 0 matched / 1 failed ]
------------------------------- Final Result!! -------------------------------
test_show_interfaces_1 : Failed
test_show_interfaces : Failed
Total No of tests passed: 0
Total No of tests failed: 2
Overall Tests failed!!!

Tests written?

Yes, will be given in next commit

[coveralls]

Pull Request Test Coverage Report for Build 258

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 46 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 92.525%

---

Files with Coverage Reduction	New Missed Lines	%
/home/travis/build/Juniper/jsnapy/lib/jnpr/jsnapy/jsnapy.py	1	94.62%
/home/travis/build/Juniper/jsnapy/lib/jnpr/jsnapy/check.py	45	85.56%

Totals
Change from base Build 257:	-0.1%
Covered Lines:	2624
Relevant Lines:	2836

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 258

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 46 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 92.525%

---

Files with Coverage Reduction	New Missed Lines	%
/home/travis/build/Juniper/jsnapy/lib/jnpr/jsnapy/jsnapy.py	1	94.62%
/home/travis/build/Juniper/jsnapy/lib/jnpr/jsnapy/check.py	45	85.56%

Totals
Change from base Build 257:	-0.1%
Covered Lines:	2624
Relevant Lines:	2836

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 259

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 42 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.02%) to 92.666%

---

Files with Coverage Reduction	New Missed Lines	%
/home/travis/build/Juniper/jsnapy/lib/jnpr/jsnapy/jsnapy.py	1	94.62%
/home/travis/build/Juniper/jsnapy/lib/jnpr/jsnapy/check.py	41	86.63%

Totals
Change from base Build 257:	0.02%
Covered Lines:	2628
Relevant Lines:	2836

---

💛 - Coveralls