Replace some explicit panics with methods

[mkroening]

No description provided.

[codecov]

Codecov Report

Merging #166 (5e49b58) into master (495d3ff) will increase coverage by 0.06%.
The diff coverage is 75.60%.

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
+ Coverage   31.02%   31.09%   +0.06%     
==========================================
  Files          15       15              
  Lines        3993     3991       -2     
==========================================
+ Hits         1239     1241       +2     
+ Misses       2754     2750       -4     

Impacted Files	Coverage Δ
src/vm.rs	28.35% <73.52%> (ø)
src/linux/uhyve.rs	53.77% <85.71%> (+1.00%)	⬆️

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[jounathaen]

LGTM
bors r+

[bors]

Build succeeded:

• Build (macOS-latest, nightly)
• Build (ubuntu-latest, nightly)
• Cargo tests (macOS-latest, nightly)
• Cargo tests (ubuntu-latest, nightly)
• Clippy
• Format check (ubuntu-latest, nightly)
• KVM Tests
• Rusty-Hermit Kernel based integration tests
• Rusty-Hermit Kernel Tests