Mir can't start if KMS is disabled (nomodeset kernel parameter)

Mir can't start if KMS is disabled (nomodeset kernel parameter).

The nomodeset option is used to diagnose kernel graphics problems and gives you a simple framebuffer instead. Xorg can deal with this and still works in low resolution, but Mir cannot even start under such conditions yet:

$ sudo mir_demo_server
[2016-08-15 11:48:43.120823] mirplatform: Found graphics driver: mir:mesa-kms (version 0.23.5)
[2016-08-15 11:48:43.120874] mirplatform: Found graphics driver: mir:mesa-x11 (version 0.23.5)
[2016-08-15 11:48:43.121189] mirserver: Starting
[2016-08-15 11:48:43.121274] mircommon: Loading modules from: /usr/lib/x86_64-linux-gnu/mir/server-platform
[2016-08-15 11:48:43.121302] mircommon: Loading module: /usr/lib/x86_64-linux-gnu/mir/server-platform/graphics-mesa-kms.so.9
[2016-08-15 11:48:43.121459] mircommon: Loading module: /usr/lib/x86_64-linux-gnu/mir/server-platform/server-mesa-x11.so.9
[2016-08-15 11:48:43.121714] mircommon: Loading module: /usr/lib/x86_64-linux-gnu/mir/server-platform/input-evdev.so.5
[2016-08-15 11:48:43.122199] mirplatform: Found graphics driver: mir:mesa-kms (version 0.23.5)
[2016-08-15 11:48:43.122228] mirplatform: Found graphics driver: mir:mesa-x11 (version 0.23.5)
ERROR: /build/mir-RyEtCF/mir-0.23.5+16.10.20160729/src/server/graphics/default_configuration.cpp(133): Throw in function mir::DefaultServerConfiguration::the_graphics_platform()::<lambda()>
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error> >
std::exception::what: Exception while creating graphics platform
ERROR: /build/mir-RyEtCF/mir-0.23.5+16.10.20160729/src/platform/graphics/platform_probe.cpp(63): Throw in function std::shared_ptr<mir::SharedLibrary> mir::graphics::module_for_device(const std::vector<std::shared_ptr<mir::SharedLibrary> >&, const mir::options::ProgramOption&)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error> >
std::exception::what: Failed to find platform for current system

Related: https://bugs.launchpad.net/mir/+bug/1118903/comments/37