Analyse following RPM build log snippet. Describe contents accurately, without speculation or suggestions for resolution.            
Your analysis must be as concise as possible, while keeping relevant information intact.
Snippet: 
EXCEPTION: [Error('Command failed: \n # /usr/bin/systemd-nspawn -q -M 80e669d707c44a65ab2880d683bc7852 -D /var/lib/mock/f41-build-side-85719-49668308-5919190/root -a -u mockbuild --capability=cap_ipc_lock --bind=/tmp/mock-resolv.h8_75ifa:/etc/resolv.conf --bind=/dev/btrfs-control --bind=/dev/mapper/control --bind=/dev/fuse --bind=/dev/loop-control --bind=/dev/loop0 --bind=/dev/loop1 --bind=/dev/loop2 --bind=/dev/loop3 --bind=/dev/loop4 --bind=/dev/loop5 --bind=/dev/loop6 --bind=/dev/loop7 --bind=/dev/loop8 --bind=/dev/loop9 --bind=/dev/loop10 --bind=/dev/loop11 --console=pipe --setenv=TERM=vt100 --setenv=SHELL=/bin/bash --setenv=HOME=/builddir --setenv=HOSTNAME=mock --setenv=PATH=/usr/bin:/bin:/usr/sbin:/sbin \'--setenv=PROMPT_COMMAND=printf "\\033]0;<mock-chroot>\\007"\' \'--setenv=PS1=<mock-chroot> \\s-\\v\\$ \' --setenv=LANG=C.UTF-8 --resolv-conf=off bash --login -c \'/usr/bin/rpmbuild -bb --noclean --target i686 --nodeps /builddir/build/SPECS/qt5-qtbase.spec\'\n', 1)]
Explains that exception happened because command /usr/bin/systemd-nspawn failed