Refactored run_command functions.

Back in the day, dumpstate.c had a simple run_command() function. Then on
Android N, dumpstate.c became dumpstate.cpp and that function multiplied into:

- run_command()
- run_command_as_shell()
- run_command_always()

Not only these 3 commands were pretty much copy-and-pasted, but they
didn't take advantage of C++ features (such as std::vector and
std::string).

This CL refactor them into a single runCommand() function that takes an
optional CommandOptions argument to set its behavior. Examples:

// Run as shell
   runCommand("DUMPSYS MEMINFO", {"meminfo", "-a"},
              CommandOptions::WithTimeout(90).DropRoot().Build());

// Run always, as shell
   runCommand(nullptr, am, CommandOptions::WithTimeout(20).Build());

The legacy run_command() is still available since it's used by
device-specific dumpstate_board() implementations, but it will
eventually go away as well.

This change also:
- Refactored run_dumpsys() into runDumpsys().
- Added a .clang-format file (initially equals to dumpsys's).
- Renamed the variable names on those commands according to the style guide.

BUG: 26379932
Test: manual

Change-Id: Ie045eb2fb825e68088d231129044c59e61450d99