cluster.max_shards_per_node derives shard count from default not template settings

[mark54g]

Elasticsearch version (bin/elasticsearch --version):
Tested in version 6.x. May hit other versions

Plugins installed: []
N/A

JVM version (java -version):
N/A

OS version (uname -a if on a Unix-like system):
N/A

Description of the problem including expected versus actual behavior:

Steps to reproduce:

Have too many shards, and create index or reindex.

You will receive a warning that this will add [10] shards, irrespective of the number that would be created due to the template for that index setting those shards to a different number.

cluster.max_shards_per_node checks the default number of shards to be created, not the template settings for the index.

Provide logs (if relevant):

[elasticmachine]

Pinging @elastic/es-core-features