fix(Checkbox): Set checked value correctly

[boaz0]

What:

closes #1959

I first realized that the controlled Checkbox example is wrong: event.target.name is not set and so the state can be {check1: false, check2: false, '': false} or {check1: false, check2: false, '': true}.

After fixing it by adding the name attribute to the Checkbox components the first time I checked one of the boxes I got the following error/warning message:

Warning: A component is changing an uncontrolled input of type checkbox to be controlled.
Input elements should not switch from uncontrolled to controlled (or vice versa).
Decide between using a controlled or uncontrolled input element for 
the lifetime of the component. More info: https://fb.me/react-controlled-components
    in input (created by Checkbox)
    in div (created by Checkbox)
    in Checkbox (created by ControlledCheckbox)
    in ControlledCheckbox (created by ErrorBoundary)
    in ErrorBoundary (created by Context.Consumer)

It looks like the expression isChecked || checked will return undefined if isChecked is false and so when checking the box that expression changed to true which causes the component to turn to be controlled.

//cc @dlabrecq
fixes https://github.com/project-koku/koku-ui/issues/841

[patternfly-build]

PatternFly-React preview: https://1929-pr-patternfly-react-patternfly.surge.sh

[codecov-io]

Codecov Report

Merging #1929 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1929      +/-   ##
==========================================
+ Coverage   82.63%   82.64%   +0.01%     
==========================================
  Files         624      624              
  Lines        6875     6879       +4     
  Branches       93       94       +1     
==========================================
+ Hits         5681     5685       +4     
  Misses       1154     1154              
  Partials       40       40

Flag	Coverage Δ
#patternfly3	84.89% <ø> (ø)	⬆️
#patternfly4	79.39% <100%> (+0.02%)	⬆️
#patternflymisc	95.68% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
...-4/react-core/src/components/Checkbox/Checkbox.tsx	90.32% <100%> (+1.43%)	⬆️

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[tlabaj]

@boaz0 can you add issue number to the description

[boaz0]

Done 👍

[tlabaj]

LGTM

[boaz0]

Thanks @tlabaj & @dlabrecq