[ZEPPELIN-1261] Bug fix in z.show() for matplotlib graphs

[bustios]

What is this PR for?

Bug fix in z.show() for matplotlib graphs and code refactoring

What type of PR is it?

Bug Fix

What is the Jira issue?

ZEPPELIN-1261

How should this be tested?

%python
import matplotlib.pyplot as plt

x = [1,2,3,4,5]
y = [6,7,8,9,0]

plt.plot(x, y, marker="o")
z.show(plt, height="20em")
plt.close()

%python
import matplotlib.pyplot as plt

x = [1,2,3,4,5]
y = [6,7,8,9,0]

plt.plot(x, y, marker="o")
z.show(plt, height="300px")
plt.close()

Screenshots (if appropriate)

Questions:

• Does the licenses files need update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[bzz]

Looks great to me, thank you @bustios !

Just FYI - in case of CI failure, If contributor posts failure logs from TravisCI, that helps to improve project stability a lot as it makes people fix flaky tests, infrastructural problems, etc.

Current CI failure is due to flaky ZeppelinSparkClusterTest.sparkRTest test:

[INFO] Zeppelin: Server ................................... FAILURE [03:05 min]
....
Results :

Failed tests: 
  ZeppelinSparkClusterTest.sparkRTest:116 expected:<[[1] 3]> but was:<[<pre><code>Error in getSparkSession(): SparkSession not initialized
</code></pre>

<pre><code>Error in (function (classes, fdef, mtable) : unable to find an inherited method for function 'count' for signature '&quot;function&quot;'
</code></pre>]>

Tests run: 65, Failures: 1, Errors: 0, Skipped: 0

same as #1249 #1051 #1160 #1043 #943 and #835. Logged under ZEPPELIN-1271

Merging to master if there is no further discussion

[bustios]

I see. Thanks for your help and information @bzz. I'll keep it in mind for subsequent PRs

[bzz]

Sounds great! Apparently CI failure has been addressed in #1259 as well