cleaned istanbul and coverage util

[liranmauda]

Explain the changes

• cleaned istanbul and coverage util

We are not using the coverage for a few years now.
We should clean it.

we can use the jest tests also for coverage:
it will output:

------------------------------|---------|----------|---------|---------|----------------------------------------------------------------------------------------------------------------------------------------------
File                          | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
------------------------------|---------|----------|---------|---------|----------------------------------------------------------------------------------------------------------------------------------------------
All files                     |      33 |    29.32 |   33.66 |   32.96 |
 noobaa-core                  |    1.81 |        0 |       0 |    1.83 |
  config.js                   |    1.81 |        0 |       0 |    1.83 | 35-797
 noobaa-core/src/server/utils |   93.45 |    91.02 |   94.73 |   93.63 |
  bucket_diff.js              |   93.45 |    91.02 |   94.73 |   93.63 | 104-120
 noobaa-core/src/util         |   33.33 |    15.59 |   20.25 |   34.26 |
  console_wrapper.js          |   72.72 |      100 |      25 |   72.72 | 22,26,30,34,38,52
  debug_config.js             |   41.66 |        0 |       0 |   41.66 | 40-47
  debug_module.js             |   46.06 |    23.74 |   35.29 |    47.3 | 31-33,68,78-79,86,97-108,122,216,224,242,268-426,457-458,469-478,490-500,514-520,543-546,552,558,562,566,570,574,578-581,586,590,594,605,608
  linked_list.js              |   12.67 |        4 |    5.88 |   12.67 | 18-133
  lru.js                      |   15.78 |        0 |    9.09 |   16.07 | 17-20,43-128
  nb_native.js                |   11.49 |        0 |       0 |   12.34 | 22-138
------------------------------|---------|----------|---------|---------|----------------------------------------------------------------------------------------------------------------------------------------------
Test Suites: 1 passed, 1 total
Tests:       59 passed, 59 total
Snapshots:   0 total
Time:        2 s