Refactor/replace curp client

[iGxnon]

Base on #582 , replace CurpClient

Please briefly answer these questions:

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)

• what changes does this pull request make?

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)

[codecov]

Codecov Report

Attention: 298 lines in your changes are missing coverage. Please review.

Comparison is base (fa656ad) 64.40% compared to head (a4fe329) 79.74%.
Report is 52 commits behind head on master.

Files	Patch %	Lines
curp/src/client/unary.rs	86.88%	67 Missing ⚠️
curp/src/rpc/connect.rs	60.71%	33 Missing ⚠️
curp/src/client/tests.rs	92.59%	30 Missing ⚠️
xline/src/server/kv_server.rs	45.45%	18 Missing ⚠️
xline/src/storage/compact/mod.rs	0.00%	16 Missing ⚠️
curp/src/server/mod.rs	54.54%	15 Missing ⚠️
xline/src/storage/compact/periodic_compactor.rs	41.66%	14 Missing ⚠️
xline/src/storage/compact/revision_compactor.rs	46.15%	14 Missing ⚠️
xline-client/src/clients/kv.rs	67.50%	13 Missing ⚠️
curp/src/client/retry.rs	92.50%	12 Missing ⚠️
... and 15 more

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #585       +/-   ##
===========================================
+ Coverage   64.40%   79.74%   +15.34%     
===========================================
  Files         105      157       +52     
  Lines       18802    21994     +3192     
  Branches    18802        0    -18802     
===========================================
+ Hits        12109    17539     +5430     
+ Misses       5955     4455     -1500     
+ Partials      738        0      -738     

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[themanforfree]

LGTM