add adb.getprop() and adb.getSystemImageCapability()

[NeoTheThird]

preparations for ubports/ubports-installer#2505

[codecov]

Codecov Report

Merging #61 (6decdbe) into master (51e20a5) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
+ Coverage   98.59%   98.61%   +0.01%     
==========================================
  Files           8        8              
  Lines         426      432       +6     
==========================================
+ Hits          420      426       +6     
  Misses          6        6              

Impacted Files	Coverage Δ
src/adb.js	97.26% <100.00%> (+0.07%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 51e20a5...6decdbe. Read the comment docs.