BaseLinuxDevice: Tidied up the way binaries are handled

Added:
get_binary_path: Checks binary_directory for the wanted binary, if
                 if its not there, it will use which to find a
                 system one. returns the full path

install_if_needed: will install a binary only if it is not present.

Changes:
 - Busybox is now deployed to non-rooted devices
 - is_installed has now been removed as the new functions supersede it
 - binaries will now always be installed to `binaries_directory` and
   not system folders.
 - updated workloads to use these new functions
   - rt-app and sysbench might still need work

wlauto/instrumentation/trace_cmd/__init__.py

@@ -164,11 +164,12 @@ class TraceCmdInstrument(Instrument):
             raise InstrumentError('trace-cmd instrument cannot be used on an unrooted device.')
         if not self.no_install:
             host_file = context.resolver.get(Executable(self, self.device.abi, 'trace-cmd'))
-            self.trace_cmd = self.device.install_executable(host_file)
+            self.trace_cmd = self.device.install(host_file)
         else:
-            if not self.device.is_installed('trace-cmd'):
+            self.trace_cmd = self.device.get_binary_path("trace-cmd")
+            if not self.trace_cmd:
                 raise ConfigError('No trace-cmd found on device and no_install=True is specified.')
-            self.trace_cmd = 'trace-cmd'
+
         # Register ourselves as absolute last event before and
         #   first after so we can mark the trace at the right time
         signal.connect(self.insert_start_mark, signal.BEFORE_WORKLOAD_EXECUTION, priority=11)