adt-installer: add warning if MACHINE is not set in adt-installer.conf
Since the MACHINE can now be specified in adt-installer.conf, in order to
install the proper toolchain and environment script for the given
machine, add a sanity checking at the beginning to make sure MACHINE is
set for the wanted architecture.
Also:
* uncomment the x86 target variables, in adt-installer.conf, in order
to have qemux86 MACHINE set, by default, and also the sysroot
installed (since it doesn't make much sense to install the toolchain
without a target sysroot);
* remove 'sudo' when creating relocate_sdk_tmp.py because the file is
created in adt-installer directory;
