meson.bbclass: Close the log file after reading

This fixes warnings like:

    WARNING: package-name-0.0.1-r0 do_configure: <string>:164: ResourceWarning:
    unclosed file <_io.TextIOWrapper
    name='/source_directory/build/tmp/work/arch/package-name/0.0.1-r0/package-name-0.0.1//meson-logs/meson-log.txt'
    mode='r' encoding='UTF-8'>

Signed-off-by: Anton Eliasson <anton.eliasson@axis.com>
Reviewed-by: Ola x Nilsson <ola.x.nilsson@axis.com>
Signed-off-by: Anton Eliasson <anton.eliasson@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>