Set user agent string for request module

[dgolovin]

This fix allows to filer devsuite installer requests to download manager rest interface from requests from browser or other services

[codecov-io]

Codecov Report

Merging #1263 into master will decrease coverage by 0.38%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1263      +/-   ##
==========================================
- Coverage   93.45%   93.06%   -0.39%     
==========================================
  Files          43       43              
  Lines        4596     4672      +76     
  Branches      504      792     +288     
==========================================
+ Hits         4295     4348      +53     
- Misses        301      305       +4     
- Partials        0       19      +19

Impacted Files	Coverage Δ
browser/services/request.js	100% <100%> (ø)	:arrow_up:
browser/model/devstudio-autoinstall.js	97.29% <0%> (-2.71%)	:arrow_down:
browser/pages/account/controller.js	97.93% <0%> (-2.07%)	:arrow_down:
browser/model/helpers/downloader.js	96.13% <0%> (-1.66%)	:arrow_down:
browser/model/che.js	95% <0%> (-1.62%)	:arrow_down:
browser/model/cdk.js	98.71% <0%> (-1.29%)	:arrow_down:
browser/model/devstudio-p2-zip.js	64.4% <0%> (-1.12%)	:arrow_down:
browser/model/devstudio-p2.js	81.66% <0%> (-1.1%)	:arrow_down:
browser/model/jbossfusekaraf.js	99.01% <0%> (-0.99%)	:arrow_down:
browser/model/devstudio-central-p2-zip.js	60.31% <0%> (-0.98%)	:arrow_down:
... and 22 more

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