This change:
* Switches BootJars/UpdatableBootJars fields of config.productVariables
from []string to ConfiguredJarList.
* Updates BootJars() method to simply concatenate the jars list from
the BootJars/UpdatableBootJars fields.
* Adds an UnmarshalJSON(..) method to ConfiguredJarList to support
unmarshalling from a single string array to avoid having to change the
format of the JSON file from which the configuration is loaded.
* Adds some additional calls to ConfiguredJarList(..) in tests to
convert from []string to ConfiguredJarList. They pass nil as the
ctx argument as there is no suitable PathContext which will cause any
errors to be thrown using panic. That is reasonable for hard coded
values in tests. A follow up change will clean up the calls to
ConfiguredJarList(..).
Bug: 171479578
Test: m nothing
Change-Id: I59b94dafb479ccd8f0471ed802be175af57be271
69d1fb1e39