Currently, Evergreen tasks that don't have the storage engine in their names could be of one of the following categories.
1. use mmapv1, specified in evergreen.yml
2. don't use a storage engine
3. use the default storage engine
4. use a storage engine specified in the suite configuration file.

In particular, 1 and 3 are contradictory and could lead to issues like the one fixed in SERVER-24959

It'd be nice to reflect the storage engine more explicitly in the task names and distinguish between the above 4 types of tasks.

For future reference, here's a list of tasks that currently don't specify a storage engine explicitly in evergreen.yml.

aggregation_auth
dur_jscore_passthrough
jsCore_auth
replicasets_auth
replicasets_legacy
replication_auth
sharding_auth

failpoints
failpoints_auth
durability
disk
httpinterface
integration_tests_*
mongosTest
mmap
multiversion
sasl
sharding_last_stable_mongos
ssl
sslSpecial