[CLASS][QEMU-LOCAL][ADD] add support for running a local installation of qemu

This commit:

• adds the qemuboot-local recipe, which deploys runqemu and its hard dependencies to DEPLOY_DIR_IMAGE
• inherits the qemuboot-local bbclass, which does two things:
  • adds qemu dependencies such as qemu-helper-native and ovmf on x86
  • deploys the *.local.qemuboot.conf script which is a patched version of the *.qemuboot.conf files produces by the qemuboot bbclass

This allows running core-image-minimal in two ways:

• from a bitbake environment (after sourcing the project setup script):

runqemu [slirp] [nographic]         # arm
runqemu [slirp] [nographic] [ovmf]  # x86

• directly from the deploy directory (DEPLOY_DIR_IMAGE), with a suitable qemu system installed in /usr/bin, without sourcing the bitbake environment script:

PATH="$PWD:$PATH" runqemu [slirp] [nographic]        # arm
PATH="$PWD:$PATH" runqemu [slirp] [nographic] [ovmf] # x86