Hide storageadapter

[rshym]

Changes introduced by this PR are:

• aos-vis: Rework handling of AOS_VIS_PLUGINS
• INSTALL.txt: Remove "storageadapter" as not relevant

[rshym]

Tested by following cases:

a) Expected configuration. Test OK, aos-vis works as expected.
XT_USE_VIS_SERVER = "true"
AOS_VIS_PLUGINS = "renesassimulatoradapter"

b) Plugin is not specified. Test OK, aos-vis works as expected.
XT_USE_VIS_SERVER = "true"
#AOS_VIS_PLUGINS = "renesassimulatoradapter"

c) VIS is not enabled. Test OK, no aos-vis installed in DomD.
#XT_USE_VIS_SERVER = "true"
#AOS_VIS_PLUGINS = "renesassimulatoradapter"

d) Double definition of plugin. Test OK, aos-vis works as expected.
XT_USE_VIS_SERVER = "true"
AOS_VIS_PLUGINS = "renesassimulatoradapter storageadapter"

[rshym]

Reviewer is added.

[arminn]

LGTM