Improve error message in update.sh when updater is corrupt.

[winder]

Summary

A user reported a strange and not very helpful error message. This was due to incomplete error handling in the bash script relating to a truncated updater binary.

The current workaround for this is to delete the updater binary and trigger update.sh to re-download it, but this is not obvious and I wouldn't expect any user to reach that conclusion.

This fix adds error handling in case updater fails and should fix this particular failure.

Here is the error message:

Current Version = 8590458880
Latest Version =
./update.sh: line 250: [: 8590458880: unary operator expected
New version found
Update Downloaded to /tmp/tmp.QlV71NLGFr/.tar.gz
Expanding update...
tar (child): /tmp/tmp.QlV71NLGFr/.tar.gz: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now
*** UPDATE FAILED: Error expanding update ***

Test Plan

Ran some tests against a directory, empty file, and regular file in my shell:

will@arendelle:~/go/src/github.com/algorand/go-algorand/cmd/updater$ [[ -f dir && -s dir ]]
will@arendelle:~/go/src/github.com/algorand/go-algorand/cmd/updater$ echo $?
1
will@arendelle:~/go/src/github.com/algorand/go-algorand/cmd/updater$ [[ -f empty && -s empty ]]
will@arendelle:~/go/src/github.com/algorand/go-algorand/cmd/updater$ echo $?
1
will@arendelle:~/go/src/github.com/algorand/go-algorand/cmd/updater$ [[ -f util.go && -s util.go ]]
will@arendelle:~/go/src/github.com/algorand/go-algorand/cmd/updater$ echo $?
0

[codecov-commenter]

Codecov Report

Merging #2766 (ad3640b) into master (80bd5ed) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2766      +/-   ##
==========================================
- Coverage   47.14%   47.10%   -0.04%     
==========================================
  Files         349      349              
  Lines       56322    56322              
==========================================
- Hits        26553    26531      -22     
- Misses      26800    26818      +18     
- Partials     2969     2973       +4     

Impacted Files	Coverage Δ
ledger/roundlru.go	90.56% <0.00%> (-5.67%)	⬇️
network/wsPeer.go	72.14% <0.00%> (-2.79%)	⬇️
agreement/cryptoVerifier.go	75.73% <0.00%> (-2.21%)	⬇️
agreement/proposalManager.go	96.07% <0.00%> (-1.97%)	⬇️
data/transactions/verify/txn.go	45.08% <0.00%> (-0.90%)	⬇️
catchup/service.go	69.35% <0.00%> (-0.78%)	⬇️
ledger/acctupdates.go	62.55% <0.00%> (+0.08%)	⬆️

---

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[tsachiherman]

could you please check this line with shellcheck ?

[winder]

Shellcheck doesn't have anything to say about this line