Ensure that --machine-account-address flag is valid Flow address

[jordanschalm]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1226 (5faf3eb) into master (be8fae8) will increase coverage by 0.01%.
The diff coverage is 57.89%.

@@            Coverage Diff             @@
##           master    #1226      +/-   ##
==========================================
+ Coverage   55.81%   55.83%   +0.01%     
==========================================
  Files         484      484              
  Lines       29770    29788      +18     
==========================================
+ Hits        16615    16631      +16     
+ Misses      10890    10889       -1     
- Partials     2265     2268       +3     

Flag	Coverage Δ
unittests	55.83% <57.89%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/bootstrap/cmd/machine_account.go	62.74% <55.55%> (-3.93%)	⬇️
cmd/bootstrap/cmd/keys.go	59.15% <100.00%> (ø)
cmd/util/ledger/migrations/storage_v4.go	41.56% <0.00%> (-0.61%)	⬇️
...sus/approvals/assignment_collector_statemachine.go	53.84% <0.00%> (+6.73%)	⬆️

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