ch_integration_tests: Add direct kernel boot test

Relying on the newly added KernelType enum, this patch expand the list
of valid types with "Direct", to represent the direct kernel boot type.
A new test is created to leverage this new type and make sure direct
kernel boot is properly validated through the integration test suite.

The kernel is built from the Cloud Hypervisor kernel branch.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

Author: Sebastien Boeuf

Jenkinsfile

@@ -31,7 +31,7 @@ pipeline{
 					}
 					stage ('Install dependencies') {
 						steps {
-							sh "sudo apt update && sudo apt install -y meson ninja-build gcc libxml2-utils xsltproc python3-docutils libglib2.0-dev libgnutls28-dev libxml2-dev libnl-3-dev libnl-route-3-dev libyajl-dev make libcurl4-gnutls-dev qemu-utils libssl-dev mtools libudev-dev libpciaccess-dev"
+							sh "sudo apt update && sudo apt install -y meson ninja-build gcc libxml2-utils xsltproc python3-docutils libglib2.0-dev libgnutls28-dev libxml2-dev libnl-3-dev libnl-route-3-dev libyajl-dev make libcurl4-gnutls-dev qemu-utils libssl-dev mtools libudev-dev libpciaccess-dev flex bison libelf-dev"
 						}
 					}
 					stage ('Configure') {