Refactor time related utility methods

[ypadron-in]

PR #2113 exposed failures in tests of DefaultMailCreator class: createErrorEmail, createFirstErrorMessage and createSuccessEmail.

Failures were related to an early initialization of a static SimpleDateFormat object inside the class. As a result of this, changes to the default timezone made later in the tests did not have an effect on that object.

This PR solves this issue by eliminating the use of non-immutable static fields in the utility method that formats dates. It also moves time related utility methods from across the project into a newly created TimeUtils class.

[codecov]

Codecov Report

Merging #2164 into master will increase coverage by 0.09%.
The diff coverage is 27.33%.

@@             Coverage Diff              @@
##             master    #2164      +/-   ##
============================================
+ Coverage     33.81%   33.91%   +0.09%     
- Complexity     2815     2819       +4     
============================================
  Files           421      421              
  Lines         29859    29784      -75     
  Branches       3780     3767      -13     
============================================
+ Hits          10096    10100       +4     
+ Misses        18863    18787      -76     
+ Partials        900      897       -3

Impacted Files	Coverage Δ	Complexity Δ
az-core/src/main/java/azkaban/utils/Utils.java	52.44% <ø> (+7.47%)	38 <0> (-6)	⬇️
...ava/azkaban/webapp/servlet/FlowTriggerServlet.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...azkaban/webapp/servlet/AbstractAzkabanServlet.java	6.06% <0%> (-0.71%)	6 <0> (ø)
...src/main/java/azkaban/webapp/servlet/WebUtils.java	24.24% <0%> (ø)	2 <0> (?)
...n/java/azkaban/webapp/servlet/ScheduleServlet.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...mmon/src/main/java/azkaban/scheduler/Schedule.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../src/main/java/azkaban/execapp/TriggerManager.java	12.82% <0%> (ø)	3 <0> (ø)	⬇️
.../main/java/azkaban/trigger/builtin/SlaChecker.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../azkaban/flowtrigger/TriggerInstanceProcessor.java	89.7% <100%> (ø)	12 <0> (ø)	⬇️
.../src/restli/java/azkaban/restli/ResourceUtils.java	16.66% <100%> (-4.39%)	1 <0> (ø)
... and 8 more

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[coveralls]

Pull Request Test Coverage Report for Build 4438

• 51 of 149 (34.23%) changed or added relevant lines in 12 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.1%) to 37.044%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
azkaban-common/src/main/java/azkaban/scheduler/Schedule.java	0	1	0.0%
azkaban-exec-server/src/main/java/azkaban/execapp/TriggerManager.java	0	1	0.0%
azkaban-web-server/src/main/java/azkaban/webapp/servlet/FlowTriggerServlet.java	0	2	0.0%
azkaban-web-server/src/main/java/azkaban/webapp/servlet/LoginAbstractAzkabanServlet.java	1	3	33.33%
azkaban-web-server/src/main/java/azkaban/webapp/servlet/AbstractAzkabanServlet.java	0	4	0.0%
azkaban-web-server/src/main/java/azkaban/webapp/servlet/ScheduleServlet.java	0	5	0.0%
azkaban-common/src/main/java/azkaban/trigger/builtin/SlaChecker.java	0	8	0.0%
azkaban-web-server/src/main/java/azkaban/webapp/servlet/WebUtils.java	0	11	0.0%
az-core/src/main/java/azkaban/utils/TimeUtils.java	36	100	36.0%

Files with Coverage Reduction	New Missed Lines	%
azkaban-web-server/src/main/java/azkaban/webapp/servlet/AbstractAzkabanServlet.java	1	6.82%
azkaban-common/src/main/java/azkaban/scheduler/Schedule.java	1	0.0%

Totals
Change from base Build 4435:	0.1%
Covered Lines:	10981
Relevant Lines:	29643

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💛 - Coveralls

[burgerkingeater]

Thanks