tests: zebra_seg6local has a race condition

tests: zebra_seg6local has a race condition

The test is checking installing of seg6 routes by this
loop:

for up to 5 times:
    sharp install seg6 route
    show ip route and is it installed

The problem is that if the system is under heavy
load the installation may not have happened yet
and by immediately reinstalling the same route
the same thing could happen again.

Modify the code to pull the route installation
outside of the loop and to increase to 10 attempts
in case there is very heavy system load.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>